The present invention relates to systems and methods for diagnosing interrelated component failures in an internal combustion engine.
To improve performance, many internal combustion engines, particularly diesel engines, include a turbocharger to increase the oxygen density of the cylinder charge. Turbochargers use the engine exhaust gases to operate a turbine which in turn powers a compressor to compress intake air. Variable geometry turbochargers (VGT), which include variable nozzle turbochargers (VNT), are used to modify turbocharger characteristics over a broader engine operating range than possible with conventional turbochargers. Moveable intake or exhaust vanes (VNT) or a moveable turbine sidewall may be used to provide an appropriate amount of turbo boost pressure for current operating conditions and driver demanded engine torque.
Exhaust gas recirculation (EGR) has known advantages with respect to reducing emissions of nitrogen oxides (NOx) by reducing peak combustion temperatures within the engine cylinders. EGR systems typically include an EGR valve which diverts engine exhaust gases from the engine exhaust manifold to the engine intake manifold. This requires a pressure differential between the exhaust and intake manifolds for the gas to flow from the exhaust to the intake. Naturally aspirated engines typically create a vacuum at the intake and have a considerably higher exhaust gas pressure which easily flows any desired amount of EGR. For turbocharged engines, additional back pressure may be required to provide a sufficient pressure differential to introduce the exhaust gas into the compressed intake air. One method for controlling back pressure is to modify the geometry of a VNT or VGT.
As such, to achieve the benefits associated with EGR, both the EGR system components and VGT system components should be in proper working order. Various diagnostics have been developed to monitor the EGR system and VGT system. However, because the systems are interrelated, it may be difficult to distinguish between component malfunctions associated with the EGR system from component malfunctions associated with the VGT system. This may lead to additional troubleshooting time for service and maintenance personnel when a fault occurs. In addition, corrective engine/vehicle control is more difficult to properly implement if there is a low confidence level associated with a particular generated fault code.
One object of the present invention is to provide a system and method for diagnosing an EGR system and/or VGT system related component degradation or failure.
Another object of the present invention is to provide a system and method for controlling an internal combustion engine in response to a fault associated with an EGR or VGT system component malfunction.
In carrying out the above objects and other objects, features, and advantages of the present invention, a system and method for diagnosing a component failure in an internal combustion engine having an exhaust gas recirculation system and a variable geometry turbocharger for diverting exhaust gas from an engine exhaust to an engine intake include determining whether the engine is operating in boost control mode or EGR control mode, comparing EGR flow rate to a threshold corresponding to the current control mode, generating a fault if the EGR flow rate is outside an acceptable operating range based on the threshold for a first predetermined time period, and operating in boost control mode if the fault persists for a second predetermined time period. In one embodiment, the system and method determine that the engine is operating in the EGR control mode with the threshold corresponding to a minimum EGR flow rate and determine whether the EGR flow rate exceeds the threshold. The system and method then determine whether the EGR flow rate is within an acceptable operating range of a desired EGR flow rate and generate a VGT fault if the EGR flow rate is outside of the acceptable operating range but exceeds the minimum threshold. Likewise, the system and method generate an EGR fault if the EGR flow rate is less than the minimum threshold. When operating in the boost control mode, the system and method generate an EGR fault if the EGR mass flow rate exceeds a maximum flow rate and generate a VGT fault if the turbo boost pressure is not within an acceptable operating range of a desired boost pressure.
A number of advantages are associated with the present invention. For example, the present invention provides a system and method for more accurate and reliable diagnosis and control of interrelated engine components. In particular, the present invention provides a method for differentiating between VGT and EGR related faults, activating an appropriate fault code, and/or modifying the engine control accordingly. More accurate fault codes may reduce the time necessary for service and maintenance personnel to troubleshoot and correct the root cause of any problem. In addition, engine control may be adjusted based on the fault to ameliorate the effects of a degraded or failed component.
The above features, benefits and advantages and other features, benefits and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken together with the accompanying drawings.